<?php
class foo {
    var $bar = 'I am bar.';
}

$foo = new foo();
$bar = 'bar';
$baz = array('foo', 'bar', 'baz', 'quux');
echo "{$foo->$bar}\n";
echo "{$foo->${$baz[1]}}\n";

$obj = (object) array('1' => 'foo');
var_dump(isset($obj->{'1'})); // outputs 'bool(false)'
var_dump(key($obj)); // outputs 'int(1)'
echo $obj->{'1'};


// Type 5: Relative static class method call (As of PHP 5.3.0)
class A {
    public static function who() {
        echo "A\n";
    }
}

class B extends A {
    public static function who() {
        echo "B\n";
    }
}
call_user_func(array('B', 'parent::who')); // A
echo '<br>';
// Type 6: Objects implementing __invoke can be used as callables (since PHP 5.3)
class C {
    public function __invoke($name) {
        echo 'Hello ', $name, "\n";
        echo '<br>'.'callback';
    }
}

$c = new C();
call_user_func($c, 'PHP!');

// 反引号
$output = `ls -al`;
echo "<pre>$output</pre>";
?>